Well if you think characters are developing too fast then you don't really understand what it means to write a manga, and you clearly don't know all the things that need to be taken into account.
You wanted to see Naruto and Sasuke train for like 10 yers each to get their sage/sharingan abilities... another couple of years for Kiuby mode/Ems? then the manga would have never ended... even if there was a time skip... every other character would also have to evolve... and if those 10 years would not be shown (like what the characters did all that time) you would still complain about the manga not showing it...
Kishi found a way to balance it and i think it works just fine... he can still evolve his characters while showing us their training, the abilities they develop and so on... or would you rather see a cover with "After 10 years..." and we see Naruto vs Sasuke, both pulling out jutsu that we have never seen before, and not knowing how they got them?
You wanted to see Naruto and Sasuke train for like 10 yers each to get their sage/sharingan abilities... another couple of years for Kiuby mode/Ems? then the manga would have never ended... even if there was a time skip... every other character would also have to evolve... and if those 10 years would not be shown (like what the characters did all that time) you would still complain about the manga not showing it...
Kishi found a way to balance it and i think it works just fine... he can still evolve his characters while showing us their training, the abilities they develop and so on... or would you rather see a cover with "After 10 years..." and we see Naruto vs Sasuke, both pulling out jutsu that we have never seen before, and not knowing how they got them?